In his first public comments since fleeing to Jordan with his family earlier this month, Mr Hijab said he had defected when he realised Mr al-Assad was powerless to stop the violence raging throughout Syria.

Speaking in front of a rebel flag at a press conference in Amman, Mr Riad said the shelling of urban centres by government forces had caused a ‘pain in his soul’.

‘I was powerless to stop the injustice,’ he said, confirming his support for the rebels without clarifying his plans. It is thought he will next travel to Qatar, where most senior rebels in exile are based.

Mr Riad called on ‘honourable leaders’ in Syria to follow his example and defect.

‘Syria is full of honourable officials and military leaders who are waiting for the chance to join the revolution,’ he said.

‘I urge the army to follow the example of Egypt’s and Tunisia’s armies – take the side of people.’

It is thought up to 20,000 people have died in the 17-month uprising against Mr al-Assad’s rule and the resulting government crackdown, with the battle for control of Aleppo, Syria’s second city, still raging.